<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>外部css</title>
        <link type="text/css" rel="stylesheet" href="./bootstrap-5.3.0-alpha1-dist/css/bootstrap.min.css"/>
    </head>
    <body>

        <form>
            <input type="text" name="username"/>
            <input class="btn btn-danger" type="submit">
        </form>
        <div class="container-fluid">
            <div class="row">
                <div class="col">
                    container
                </div>
                <div class="col">
                    container
                </div>
                <div class="col-4">
                    container
                </div>
                <div class="col-4">
                    container
                </div>
            </div>
        </div>
    </body>
</html>